Seed Germination in Podocarpus henkelii: An Ultrastructural and Biochemical Study

Biochemical and ultrastructural studies were undertaken on theembryo and female gametophyte of neotonous (recalcitrant) seedsof Podocarpus henkelii over a 9-d period following scarificationand incubation on a moist substrate. After 3 days incubationat 25 °C, cells of the root tip were characterized at theelectron microscope level by increased vacuolation, numerousamyloplasts and lipid mobilization. By d 6 measurable embryonicgrowth was noted and ultrastructural evidence of synthetic activitywas suggested by abundant endoplasmic reticulum (ER), ribosomesand dictyosomes. Fine-structural changes suggestive of reservemobilization were also observed in the female gametophyte. Biochemicalstudies indicated a gradual decline in lipid and protein inboth the embryo, and female gametophyte, over the 9 d of incubation.A decline in embryonic starch levels contrasted with the increaseseen in the female gametophyte at d 6. Small changes in thesugar levels of the female gametophyte contrasted with increasesin the embryonic tissues between d 3 and 6, a period coincidingwith the first records of germination. The maintenance of highmoisture contant and the evidence of metabolic activity obtainedfrom biochemical and ultrastructural observations suggest that,following scarification, the transition between maturation andgermination is characterized by a continuation of earlier syntheticactivity and reserve interconversions. Podocarpus henkelii Stapf, yellow-wood, embryo, endosperm, overgrown seed, neotonous, recalcitrant